The researchers found that while straight men are only aroused by females of the human variety, straight women are equally aroused by all human sexual activity, including lesbian, heterosexual and homosexual male sex, and at least somewhat aroused by nonhuman sex.
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"There's the possibility that genital response for women is not necessarily imbued with meaning about her sexual interests," says Chivers. She also emphasized that her findings do not imply women harbor a latent desire for lesbian sex or bestiality.

What's actually surprising is that the guys had such a selective response. You'd think just the idea of sex would be enough to get some response from most fellows.